MANILA - United Nations Special Rapporteur Agnes Callamard on Friday branded as "murder" the death of 17-year old Kian Delos Santos and called for an investigation on "all unlawful deaths."

Reposting an online article on the probe on Delos Santos' death, Callamard tweeted: "Yes, Pent Duterte, this is murder. All unlawful deaths must be investigated. To stop all murderers."

Yes, Pent Duterte, this is murder. All unlawful deaths must be investigated. To stop all murderers #Philippines https://t.co/WKKAyAE358

— Agnes Callamard (@AgnesCallamard) August 24, 2017

In a separate post with an article on Delos Santos' autopsy report, Callamard said the 11th grader's "execution" is the "latest symbol of a massive, government-led, human rights crisis."

"The autopsy also demonstrates the importance of independent and timely investigations into ALL unlawful deaths in the context of the war on drugs (and other contexts), not only those that generate public outcry," she said in a social media post.

Asked for comment, Presidential Communications Office Assistant Secretary Omar Romero said the Palace is still waiting for results of the ongoing investigation on Delos Santos' death.

"Until there is a finding by a competent court that it is murder, that we can agree...but we look forward to the results of the impartial investigation on this incident," he said.

Public outrage has been growing over Delos Santos' death, which has been decried as one of the latest killings in the name of President Rodrigo Duterte's war on illegal drugs.

Senators have begun its investigation into the teenager's death, and Philippine National Police Director General Ronald Dela Rosa vowed to probe it as well, even as he asserted that the high number of deaths in overnight anti-drug raids was "normal."

President Duterte has said those liable would be answerable and put in jail if a rubout is proven.

A CCTV footage showed that two cops in civilian clothes accosted Delos Santos towards the direction where he was killed. Witnesses also said they saw the officers blindfold and beat the teenager before the shooting. They added that Delos Santos was killed even while he was already pleading for his life.

Witnesses said they followed the cops and saw how they handed a gun to Delos Santos and instructed him to shoot then run. When he heeded these instructions, the teenager was shot dead.

According to results of the autopsy by the Public Attorneys Office (PAO) forensic laboratory, Delos Santos sustained a gunshot wound to his back, to the back of his left ear, and one inside his left ear.

The location of the gunshot wounds to his ears showed that Delos Santos was on the ground when he was shot, the office said.

This was later contradicted by the PNP Crime Laboratory, which said Delos Santos sustained two gunshot wounds to the head, in his left ear.

It confirmed the downward trajectory of the gunshots but stressed that the direction does not automatically mean that the teen was on the ground when he was shot, as claimed by a forensic scientist from PAO.

Callamard had been critical of the deaths under Duterte's watch and had sought an invitation from the government to visit the country to investigate drug-related killings.

The Philippine government last year formally sent an invitation to Callamard, but she declined this due to the conditions set by the government, including a public debate with President Rodrigo Duterte, which she said would contravene UN protocols.

She visited Manila in May to attend an academic conference on drug-related issues and grace the Commission on Human Rights' 30th anniversary celebration.

• READ: Callamard: PH narco bureau's new anti-drug strategy 'gave me hope'

Malacañang, however, said it would complain to the UN after Callamard failed to notify the government of her visit, which it said was a "clear signal" she was not interested in being objective.